18.13 The demands of college. Select a first-year college student at random and ask how difficult it was for him or her to adjust to the academic demands of college. Here are the probabilities, based on proportions from a large sample survey in 2010 of first-year students:
| Difficulty: | Very difficult | Somewhat difficult |
| Probability: | 0.05 | 0.31 |
| Difficulty: | Somewhat easy | Very easy |
| Probability: | 0.44 | 0.20 |
(a) What is the sum of these probabilities? Why do you expect the sum to have this value?
(b) What is the probability that a randomly chosen first-year college student did not find it very difficult to adjust to the academic demands of college?
(c) What is the probability that a first-year student found it very or somewhat difficult to adjust to the academic demands of college?